A typical liquid crystal display (LCD) has the advantages of portability, low power consumption, and low radiation. LCDs have been widely used in various portable information products, such as notebooks, personal digital assistants (PDAs), video cameras and the like. Furthermore, the LCD is considered by many to have the potential to completely replace CRT (cathode ray tube) monitors and televisions. A liquid crystal panel is a major component of the LCD, and generally includes a thin film transistor (TFT) array substrate, a color filter substrate opposite to the TFT array substrate, a liquid crystal layer sandwiched between the two substrates, and a sealant for adhering the two substrates together. The two substrates and the sealant cooperatively form a liquid crystal cell, which contains the liquid crystal layer.
Liquid crystal material can be put into the liquid crystal cell through either of two popular processes. One of these processes is called injection by using the capillary phenomenon. The injection process includes the following steps: coating a sealant on a first one of the two substrates, at least one opening being provided in the sealant to allow for the passage of liquid crystal therethrough; sealing the first substrate with the second substrate to create a liquid crystal cell, and hardening the sealant to enhance the strength of adhesion between the two substrates and thereby form a liquid crystal panel preform; disposing the liquid crystal panel preform in a vacuum chamber; submerging the opening in a mass of liquid crystal, whereby liquid crystal is injected into the liquid crystal cell due to a pressure differential; and sealing the opening. Thus, a liquid crystal panel is formed.
The other process is called a one drop filling (ODF) method. The ODF process includes the following steps: coating a sealant on a first one of the two substrates to form a liquid crystal cell area; filling the liquid crystal cell area with liquid crystal by using a filling device; and sealing the second substrate to the first substrate, and hardening the sealant. Thus, a liquid crystal panel is formed.
Referring to FIG. 8, a typical liquid crystal panel 10 includes a color filter (CF) substrate 11, a thin film transistor (TFT) substrate 13 parallel to the CF substrate 11, a sealant 15, and a liquid crystal layer 17 sandwiched between the two substrates 11, 13. The sealant 15 is coated on a peripheral region of the TFT substrate 13.
Referring also to FIG. 9, after the TFT substrate 13 is sealed with the CF substrate 11 by the sealant 15, the sealant 15 is hardened by irradiation with ultraviolet (UV) light. Then, the liquid crystal panel 10 is baked in an oven during a thermal-hardening process to enhance the mechanical strength of the bond between the CF substrate 11 and the TFT substrate 13.
Experimental data indicates that the mechanical strength of the bond between the CF substrate 11 and the TFT substrate 13 varies according to different hardening processes. If the sealant 15 is hardened only by UV light, the adhesion strength is 0.5 kilogram-force (Kgf). If the sealant 15 is hardened only by the baking process, the adhesion strength is 3.0 Kgf. If the sealant 15 is hardened by the UV light together with the baking process, the adhesion strength is 2.0 Kgf. From these results, it is apparent that the adhesion strength is best when the sealant 15 is hardened only by the baking process. However, if the sealant 15 is not irradiated by UV light, the liquid crystal is liable to be contaminated by the sealant 15. Therefore, in the LCD industry of late, the sealant 15 is typically treated by UV light together with the baking process.
Some modern liquid crystal displays, such as liquid crystal display televisions, are made very large. In addition, it is desired that a ratio of a display area to a non-display area is high, and that accordingly a width of the sealant 15 is minimal. For these reasons, the adhesion strength of the sealant 15 may not be sufficient, and the liquid crystal panel 10 is liable to fracture. When this happens, the liquid crystal panel 10 may malfunction or even fail altogether.
What is needed, therefore, is a liquid crystal panel that can overcome the above-described deficiencies. What is also needed is a method for fabricating such liquid crystal panel.